This invention relates to electrosurgical devices and more particularly to an improved electrosurgical unit capable of providing an unmodulated signal for cutting tissue and a modulated signal for coagulation.
High frequency oscillations have been utilized for various electrotherapeutic purposes. Some devices utilize the electrostatic field produced by a high frequency oscillator for surgery, coagulation, or sterilization of utensils. For example, U.S. Pat. No. 1,945,867 teaches the creation of such high frequency oscillatory electrostatic field which is utilized for electrotherapeutic purposes. More recently, use has been made of the high frequency electrical current produced. Electrosurgery has been carried out based upon the ability to localize and control the heating effect from such high frequency electrical current. Such electric current is localized at a sharp point, usually by means of a pointed electrode, to create a high current density which provides the intense localized power needed for tissue effect. A return electrode, usually a large plate positioned under the patient, returns the current back to the electrosurgical unit. By having a rather large return plate, the current density is dispersed, causing a low current density at the contact with the return plate.
It has been found that tissue cutting can be produced by utilizing an undamped signal, while coagulation can be achieved by utilizing a damped frequency signal. Spark gap oscillators generally produce damped waveforms while vacuum tube oscillators produce undamped waveforms. As a result, many electrosurgical devices providing both tissue cutting and tissue coagulation outputs will utilize a spark gap generated waveform for coagulation, and a vacuum tube oscillator for tissue cutting. Typical of such unit is described in U.S. Pat. No. 3,058,470. Other electrosurgical units will rather utilize a single oscillator which alternates between damped and undamped signals. For example, U.S. Pat. No. 3,261,358 provides such alternating output. Also, U.S. Pat. No. 3,478,744 provides a modulated output which finds use for both cutting and coagulation. While vacuum tube oscillators are generally preferred, many units do not use them because they are usually bulky and heavy and require a long amount of warm up time during the turn-on periods.
In general, all electrosurgical units provide a return electrode, frequently called the dispersion electrode, the indifferent plate, or the butt plate. Most such prior art units extract the oscillator output across an output transformer which has either one end, or a midpoint grounded, whereby the return plate operates as a ground plate. The use of this type of grounded output unit has created many surgical problems and numerous patient injuries. The main purpose of the return plate is to disperse the current and create a low current density contact between the patient and the return path. If the patient accidentally touches a piece of grounded metal, such as the operating table, there will occur a grounded return path at that point of contact. However, the contact point will be very small which will result in a high density current causing a burn at the contact point. Even if precautions are taken to prevent contact between the patient and the operating table, it is practically impossible to avoid complete contact, because of conductive paths provided by the spillage of blood, or saline solutions. Additionally, there generally exists capacitive paths between the patient and ground which can also cause return paths to ground with possible burns at the points of close contact between the patient and ground. In recent times where numerous monitoring units, such as EKGs, ECGs, etc., are connected to the patient during a surgical operation, the point of contact between such peripheral electrical equipment and the patient also causes the possibility of high current densities flowing at such points of contacts which may also cause burns as the current flows through the equipment to ground. A further hazard can result if the return cable to the electrosurgical unit breaks or if the return plate accidentally becomes disconnected. The current will then seek alternate ground paths through the patient. Such alternate contacts will frequently be over a very small area causing severe patient burns.
A solution has been presented to provide an isolated output unit where the return plate is ungrounded and is in fact isolated from ground. In this way, the current will not seek ground contacts as return paths since the electrosurgical unit is isolated from ground. However, it has heretofore not been possible to obtain a very good isolated output and frequently, stray pathways to ground within the unit defeated the attempted isolation.
Since the accidental disconnection of the return plate can cause burns in the patient as well as other hazardous conditions, many prior art units contain sensory warning devices to give an indication when such disconnection occurs or when the cable is broken. However, in most prior art units, even though the return plate is disconnected, the probe will still provide the high current density and continue cutting tissue, thereby continuing the possibility of burns.
Prior art electrosurgical units have also presented other problems. In many cases it is desired to provide alternately either a coagulation signal or a cutting signal. Some units have provided two separate output probes, one for coagulation and one for cutting. However, frequently, both units are simultaneously activated so that while one of the probes is being used, someone may accidentally pick up the other probe and burn their hand. Some electrosurgical units only provide a single probe for alternately supplying a cutting or a coagulating output. With these units, however, when the surgeon is utilizing the single probe, it is not possible for an assistant to provide coagulation support to the surgeon.
Another difficulty with prior art electrosurgical units is in connection with the magnitude of the coagulation or cutting output voltage. It is necessary to control the magnitude of these outputs depending upon the depth of cut, the impedance provided by the patient, and various other factors. Most units do provide some type of intensity control. However, the intensity control set for a cutting procedure may not be suitable for a coagulation procedure. As a result, it is necessary for the surgeon to reset the unit as he alternates between coagulating and cutting.
Furthermore, in providing the modulated output for coagulation purposes, most electrosurgical units provide a single level of modulation, and usually use a standard 60 cycle per second output. However, it has been found that the patient acts as a rectifier for such 60 cycle modulation and muscle spasm will result during the coagulation procedure.
Still a further problem with many eklectrosurgical units is that the switching between the coagulation and the cutting takes place at a high voltage. As a result, the possiblity of sparking exists and when using explosive chemicals there is the dangerous possiblity of an explosion occurring in the operating room.